The fixed bridge accepts JSON values only. The adapter measures the exact encoded request size, and the native cap includes JSON's worst-case sixfold escaping for every accepted string field. It exposes native UTF-8 byte offsets, capture names, iteration, and Captures::expand replacement syntax. It does not evaluate user values as Rust or JavaScript source.

Replacement uses a bounded streaming implementation of Captures::expand grammar. Load-time differential fixtures compare it with the native API, and capture references stop expanding as soon as the UTF-8 output cap is reached. The bounded bytes cross the JSON bridge as base64, so control-heavy output has a fixed 4:3 transport expansion instead of JSON's content-dependent escaping.

Flags i, m, s, U, x, and R map directly to RegexBuilder. Unicode is the crate's native default; the accepted u flag explicitly affirms that default. g selects the crate's native iterator.

The crate deliberately excludes look-around and backreferences. Compile-size, DFA-cache, pattern, subject, match, capture-row, and output limits are enforced inside the module. Replacement output is clipped only at a UTF-8 boundary.